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Re: [Re: Theory on ornithoptering and could Archie do it ?]



><<<Chris:
>
>The lack of a sternum in Archae is a bit of a red herring.  It is
>probable that the sternum was not ossified, but still allowed muscle
>attachment.  Also, the new form has a small sternum.
>
> Also it is unlikely that Archae was on the direct line to power flight,
>since it lacks a number of critical features such as ligament
>placement.>>>
>
><<Still, didn't Archaeopteryx show signs of strong muscle attachments
>furcula wise. Sorta showing where large wing muscles started at before
>working their way down. >>

I did not write the last included text.  I have made no mention of the furcula.
>
>You're pretty wrong in stating this.  Larry Martin has pointed out
>repeatedly that the furcula of Archaeopteryx and the enantiornithines
>was adapted specifically for acting as the major site of the wing
>depresser muscle, the pectoralis.  Previous work done on starling
>furculae by Jenkins et.al. show that the furcuale of modern birds acts
>as a spring-spacer, a necessary part in the wingbeat and lung
>ventilation.  There are exceptions to the rule such as falconiforms and
>parrots where the furcula is to robust for being a spring and too flimsy
>to be a spring respectively.  The main way that the furcula becomes a
>spring in modern birds is its rounded cross-section.  The rounded
>cross-section gives it more flexibility.  However,  the furcula in
>Archaeopteryx and the enantiornithines has a thin,  flat cross-section
>because the furcula is posteriorly grooved.  Why did the furcula have no
>spring in early birds?  According to Martin the design of the
>Archaeopteryx and enantiornithine furcula was evolved to support a large
>pectoralis muscle, the wing depresser.  It makes sense: in modern birds
>the furcula is not the major site for the pectoralis because of its
>spring-like nature (it can't hold much muscle),  but the Archaeopteryx
>and the enantiornithine furcula,  due to its specialized design,  is
>built specifically for accomadating a large,  hypertrophied pectoralis.
>
>So,  as you see,  the furcula of Archaeopteryx is built to hold a large
>wing depresser muscle.

This has little bearing on what I wrote, namely that the some tendon
structures amongst others ( e.g. M.supracoracoideus) of Archae implies that
it was not capable of power flight (flapping flight, yes) and so was
probably not on the direct line to birds with the ability to power fly.
FWIW I accept that Archae was capable of flapping flight, but not power
flight.

Chris

cnedin@geology.adelaide.edu.au                  nedin@ediacara.org
-------------------------------------------------------------------
Many say it was a mistake to come down from the trees, some say
the move out of the oceans was a bad idea. Me, I say the stiffening
of the notochord in the Cambrian was where it all went wrong.
It was all downhill from there.